U.S. patent number 7,112,119 [Application Number 11/400,416] was granted by the patent office on 2006-09-26 for sealed polishing pad methods.
This patent grant is currently assigned to Applied Materials, Inc.. Invention is credited to Dominic J. Benvegnu, Jeffrey Drue David, David J. Lischka, Bogdan Swedek.
United States Patent |
7,112,119 |
Swedek , et al. |
September 26, 2006 |
Sealed polishing pad methods
Abstract
A polishing pad, polishing system, method of making a polishing
pad and method of using a polishing pad. The polishing pad includes
a polishing layer having a polishing surface, a backing layer with
an aperture and a first portion that is permeable to liquid, and a
sealant that penetrates a second portion of the backing layer
adjacent to and surrounding the aperture such that the second
portion is substantially impermeable to liquid. The aperture is
positioned below a substantially fluid-impermeable element.
Inventors: |
Swedek; Bogdan (Cupertino,
CA), Lischka; David J. (San Jose, CA), David; Jeffrey
Drue (San Jose, CA), Benvegnu; Dominic J. (La Honda,
CA) |
Assignee: |
Applied Materials, Inc. (Santa
Clara, CA)
|
Family
ID: |
37018839 |
Appl.
No.: |
11/400,416 |
Filed: |
April 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11213623 |
Aug 26, 2005 |
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Current U.S.
Class: |
451/6; 451/533;
51/307 |
Current CPC
Class: |
B24B
37/205 (20130101); B24D 18/00 (20130101) |
Current International
Class: |
B24B
7/00 (20060101) |
Field of
Search: |
;51/297,307,308
;451/5,6,283,285,526,533 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ackun, Jr.; Jacob K.
Attorney, Agent or Firm: Fish & Richardson
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional (and claims the benefit of
priority under 35 USC 120) of U.S. patent application Ser. No.
11/213,623, filed on Aug. 26, 2005. The disclosure of the prior
application is considered part of (and is incorporated by reference
in) the disclosure of this application.
Claims
What is claimed is:
1. A method of making a polishing pad, comprising: securing a
polishing layer with a polishing surface to a backing layer with a
first portion that is permeable to liquid; forming an aperture in
the backing layer aligned with a substantially fluid-impermeable
element above the backing layer; and applying a sealant to
penetrate a second portion of the backing layer adjacent to and
surrounding the aperture such that the second portion is
substantially impermeable to liquid.
2. The method of claim 1, further comprising forming a window from
the polishing surface to a bottom surface of the polishing pad, the
window including the aperture in the backing layer.
3. The method of claim 2, wherein the substantially
fluid-impermeable element is substantially transparent and the
window comprises the substantially fluid-impermeable element.
4. The method of claim 3, wherein forming the window molding the
fluid-impermeable element into the polishing layer.
5. The method of claim 4, wherein the fluid-impermeable element is
molded into the polishing layer before the polishing layer is
secured to the backing layer.
6. The method of claim 3, wherein forming the window comprises
adhesively attaching the fluid-impermeable element to the backing
layer.
7. The method of claim 6, wherein the fluid-impermeable element is
attached to the backing layer after the polishing layer is secured
to the backing layer.
8. The method of claim 3, wherein the sealant is applied before the
window is completed.
9. The method of claim 3, wherein the sealant is applied after the
window is completed.
10. The method of claim 1, further comprising curing the
sealant.
11. The method of claim 1, wherein the sealant comprises
silicone.
12. The method of claim 1, wherein the backing layer comprises a
foam.
13. The method of claim 1, wherein the backing layer comprises a
fibrous mat.
Description
BACKGROUND
This present invention relates to chemical mechanical
polishing.
An integrated circuit is typically formed on a substrate by the
sequential deposition of conductive, semiconductive or insulative
layers on a silicon wafer. One fabrication step involves depositing
a filler layer over a non-planar surface, and planarizing the
filler layer until the non-planar surface is exposed. For example,
a conductive filler layer can be deposited on a patterned
insulative layer to fill the trenches or holes in the insulative
layer. The filler layer is then polished until the raised pattern
of the insulative layer is exposed. After planarization, the
portions of the conductive layer remaining between the raised
pattern of the insulative layer form vias, plugs and lines that
provide conductive paths between thin film circuits on the
substrate. In addition, planarization is needed to planarize the
substrate surface for photolithography.
Chemical mechanical polishing (CMP) is one accepted method of
planarization. This planarization method typically requires that
the substrate be mounted on a carrier or polishing head. The
exposed surface of the substrate is placed against a rotating
polishing disk pad or belt pad. The polishing pad can be either a
"standard" pad or a fixed-abrasive pad. A standard pad has a
durable roughened surface, whereas a fixed-abrasive pad has
abrasive particles held in a containment media. The carrier head
provides a controllable load on the substrate to push it against
the polishing pad. A polishing liquid, which can include abrasive
particles, is supplied to the surface of the polishing pad.
In general, there is a need to detect when the desired surface
planarity or layer thickness has been reached or when an underlying
layer has been exposed in order to determine whether to stop
polishing. Several techniques have been developed for the in-situ
detection of endpoints during the CMP process. For example, an
optical monitoring system for in-situ measuring of uniformity of a
layer on a substrate during polishing of the layer has been
employed. The optical monitoring system can include a light source
that directs a light beam toward the substrate during polishing, a
detector that measures light reflected from the substrate, and a
computer that analyzes a signal from the detector and calculates
whether the endpoint has been detected. In some CMP systems, the
light beam is directed toward the substrate through a window in the
polishing pad.
SUMMARY
The invention provides methods and apparatus for sealing a portion
of a polishing pad to prevent liquid from collecting on a bottom
surface of a window.
In one aspect, the invention is directed to a polishing pad for use
in a chemical mechanical polishing system. The polishing pad
includes a polishing layer having a polishing surface. a backing
layer including a first portion that is permeable to liquid, a
window from the polishing surface to a bottom surface of the
polishing pad, and a sealant. The window includes a transparent
portion that is substantially impermeable to liquid secured to the
polishing pad and an aperture in the backing layer aligned with the
transparent portion and positioned on a side of the transparent
portion opposite the polishing surface. The sealant penetrate a
second portion of the backing layer adjacent to and surrounding the
aperture such that the second portion is substantially impermeable
to liquid.
Implementations of the invention may include one or more of the
following features. The backing layer may be a foam. The sealant
may be silicone. The polishing layer may be generally impermeable
to liquid. A top surface of the transparent portion may be coplanar
with the polishing surface. A bottom surface of the transparent
portion may be coplanar with a lower surface of the polishing
layer. The first portion may extends adjacent to an outer
peripheral edge of the backing layer. A recess may be formed in the
lower surface of the transparent portion.
In one aspect, the invention is directed to a polishing system. The
polishing system includes a polishing pad, a platen, and a
monitoring module. The polishing pad includes a polishing layer
having a polishing surface and a backing layer with an aperture and
a first portion that is permeable to liquid. The aperture is
positioned below a substantially fluid-impermeable element, and a
sealant that penetrates a second portion of the backing layer
adjacent to and surrounding the aperture such that the second
portion is substantially impermeable to liquid. The platen supports
the polishing pad and includes a second recess, and the monitoring
module is positioned in the recess. A volume is formed at least in
part between a lower surface of the fluid-impermeable element and
an upper surface of the optical monitoring module.
Implementations of the invention may include one or more of the
following features. The monitoring module may be an optical
monitoring module and fluid-impermeable element may be transparent.
A purge system may direct a purge gas into the volume and/or draw
fluid out of the volume. The purge gas may include clean dry air,
nitrogen, or inert gas. The purge system may include an exit
passage connected to an external environment. A portion of the
monitoring module may extend into the polishing pad. The sealant
may be silicone. The fluid-impermeable element may be the polishing
layer.
In another aspect, the invention is directed to a method of making
a polishing pad. The method includes securing a polishing layer
with a polishing surface to a backing layer with a first portion
that is permeable to liquid, forming a window from the polishing
surface to a bottom surface of the polishing pad, and applying a
sealant. The window includes a transparent portion that is
substantially impermeable to liquid secured to the polishing pad
and an aperture in the backing layer aligned with the transparent
portion and positioned on a side of the transparent portion
opposite the polishing surface. The sealant penetrates a second
portion of the backing layer adjacent to and surrounding the
aperture such that the second portion is substantially impermeable
to liquid.
Implementations of the invention may include one or more of the
following features. The sealant may be applied after the aperture
in the backing layer is formed, after the window is formed, or
after the polishing layer is secured to the backing layer.
The invention can provide one or more of the following advantages.
Collection of liquid on the bottom surface of the window, such as
by condensation or fogging, can be reduced. This can improve
optical signal strength, thus reducing noise, and thereby improve
endpoint detection reliability.
The details of one or more embodiments of the invention are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages of the invention will be apparent
from the description and drawings.
DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic side view, partially cross-sectional, of a
chemical mechanical polishing station with a polishing pad
according to the present invention.
FIG. 2 is an enlarged cross-sectional view of a portion of the
polishing pad on a platen.
FIG. 3 is a schematic bottom view of the polishing pad.
Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
As shown in FIG. 1, one or more substrates 10 can be polished by a
CMP apparatus 20. A description of a suitable polishing apparatus
20 can be found in U.S. Pat. No. 5,738,574, the entire disclosure
of which is incorporated herein by reference.
The polishing apparatus 20 includes a rotatable disk-shaped platen
24 on which is placed a polishing pad 30. The polishing pad 30 can
be secured to the platen 24, e.g., by a layer of adhesive. The
polishing pad 30 can be a two-layer polishing pad with an outer
cover layer or polishing layer 32 that provides a polishing surface
36, and a backing layer 34. In general, although the outer
polishing layer is roughened and can transport slurry, it is
generally fluid-impermeable. The outer polishing layer 32 may be a
cast polyurethane with fillers, such as a layer of IC-1000 from
Rodel. In addition, the polishing The backing layer 34 is typically
softer than the polishing layer 32, and may be formed from a foam
or fibrous mat, such as a layer of PORON, e.g., PORON 4701-30 from
Rogers Corporation, or Suba-IV from Rodel, that can be
fluid-permeable. Slurry transport grooves may be formed in the
polishing surface by a milling or molding process.
The polishing station can also include a pad conditioner apparatus
to maintain the condition of the polishing pad so that it will
effectively polish substrates. During a polishing step, a polishing
liquid 38, e.g., a slurry, containing a liquid and a pH adjuster
can be supplied to the surface of polishing pad 30 by a slurry
supply port or combined slurry/rinse arm 39. The polishing liquid
38 can also include abrasive particles.
A carrier head 70 can hold the substrate 10 against the polishing
pad 30. The carrier head 70 is suspended from a support structure,
for example, a carousel, and is connected by a carrier drive shaft
74 to a carrier head rotation motor so that the carrier head can
rotate about an axis 71. In addition, the carrier head 70 can
oscillate laterally in a radial slot formed the support structure
72. In operation, the platen is rotated about its central axis 25,
and the carrier head is rotated about its central axis 71 and
translated laterally across the top surface of the polishing pad. A
description of a suitable carrier head 70 can be found in U.S.
patent application Ser. Nos. 09/470,820, 09/535,575 and 10/810,784,
filed Dec. 23, 1999, Mar. 27, 2000, and Mar. 26, 2004, the entire
disclosures of which are incorporated by reference.
A recess 26 is formed in the platen 24, and an in-situ monitoring
module 50 of an in-situ monitoring system fits into the recess 26.
The in-situ monitoring system can be an optical monitoring system,
or a combination of an optical monitoring system with another type
of monitoring system such as an eddy current monitoring system. The
in-situ monitoring module 50 can include one or more sensor
elements, which provide better resolution when they are situated
close to the substrate being polished. Examples of a sensor element
include but are not limited to an optical fiber and a ferromagnetic
core. A suitable in-situ modules is further described in commonly
owned U.S. patent application Ser. No. 09/847,867, filed on May 2,
2001, Ser. No. 10/124,507, filed on Apr. 16, 2002, Ser. No.
10/123,917, also filed on Apr. 16, 2002, and Ser. No. 10/633,276,
filed on Jul. 31, 2003, which are hereby incorporated by reference
in their entireties. In some implementations, the monitoring system
might not include an optical monitoring system. In this case, the
pad need not include a transparent portion, although the monitoring
module should be positioned below a fluid-impermeable element,
e.g., an opaque plug or the polishing layer itself.
Referring to FIGS. 2 and 3, the polishing pad can include a solid
transparent portion 42 that provides a window 40. The transparent
portion 42 can be an integral portion of the polishing pad, or it
can be an element secured, e.g., molded or adhesively attached, to
the polishing pad. In particular, the window 40 can include a
transparent portion 42 positioned in the polishing layer 32 with
generally the same thickness as the polishing layer, and an
aperture 44 in the backing layer 34 that is aligned with the
transparent portion 42. A top surface of the transparent portion 42
can be co-planar with the polishing surface 36. In addition, one or
more optional recesses can be formed in the bottom surface 46 of
the transparent portion 42 that extend partially but not entirely
through the transparent portion. In general, the material of the
transparent portion 42 should be non-magnetic and non-conductive.
The plug can be a relatively pure polymer or polyurethane, for
example, formed without fillers, or the plug can be formed of a
fluorocarbon, such as Teflon, or a polycarbonate. In an
implementation in which the window includes a rigid crystalline
portion or glass-like portion and the recess is formed in the
bottom surface of this portion by machining, the recess can be
polished so as to remove scratches caused by the machining.
Alternatively, a solvent and/or a liquid polymer can be applied to
the surfaces of the recess to remove scratches caused by machining.
The removal of scratches usually caused by machining reduces
scattering and can improve the transmittance of light through the
window.
In general, the transparent portion 42 is secured to the polishing
pad so as to prevent fluid from flowing from the polishing surface
36 into the region below the transparent surface. In one
implementation, forming the window 40 includes cutting a hole in
the polishing layer 32 and securing the transparent portion 42 in
the hole. For example, the transparent portion 42 may secured by an
adhesive to the backing layer 34 and/or to the polishing layer 32.
The adhesive can form a slurry-tight seal between the transparent
potion 42 and the polishing layer 32 and/or backing layer 34. As
another example, the transparent portion 42 can be secured by
dispensing a liquid window material into the hole and curing the
liquid to mold the transparent portion 42 in place. In another
implementation, forming the window 40 includes forming the
transparent portion 42 during fabrication of the polishing layer
32. For example, a transparent plug can be positioned in a liquid
pad material, and the liquid pad material can be cured to solidify
the polishing layer 32 around the transparent portion 42. In either
case where the transparent portion is molded to the polishing
layer, the window may be formed in a cast block of pad material
from which the polishing layer (including transparent portion) is
then cut. Where the transparent portion 42 is to be secured
directly to the polishing layer 32, the securing step can occur
before or after the polishing layer 32 is attached to the backing
layer 34.
The window 40 is situated over at least a portion of the recess 26
and the module 50. The module 50 and window 40 are positioned such
that they pass beneath substrate 10 during a portion of the
platen's rotation. In some implementations, a portion of the module
50, such as a ferromagnetic core, extends into and partially (but
not entirely) through the polishing pad 30.
Optionally, the module 50 can include a purge system to purge
liquids and gases from a volume 64 between the top surface of the
module 50 and the bottom surface of the transparent portion 42. The
purge system can include a fluid inlet line 60 coupled to a purge
gas source, and a fluid outlet line 62 that can be coupled to a
vacuum source. In general, the fluid lines 60 and 62 will extend
through the platen and through a rotary coupling to the purge gas
source and vacuum source. Although illustrated as extending through
the module 50, the fluid lines 60 and 62 can be connected directly
to the volume 64 without passing through the module 50.
Alternatively, the fluid outlet line 62 can simply extend to the
external environment, in which case the outline line may simply
pass through the platen (and not through the rotary coupling).
In operation, the purge gas can flow continuously through the
volume 64, preventing water vapor from accumulating in the volume
and thus preventing condensation or fogging on the bottom surface
of the transparent portion 42. The purge gas can be a composition,
e.g., clean dry air, nitrogen, or an inert gas, that does not
interfere with the polishing process, does not damage the polishing
pad, and does not include vapor which might condense.
One potential problem is that, if the backing layer 34 is
fluid-permeable, the suction generated by the fluid outline line 62
can draw liquid from the edge of the backing layer into the volume
64. This can result in condensation or fogging, even if a purge gas
is flowing through the volume 64.
To address this issue, a portion 48 of the backing layer 34 can be
made substantially impermeable to liquid so that liquid will not
reach the volume 64. In particular, a portion 48 of the backing
layer immediately adjacent the aperture 44 can have a permeability
much lower than that of the remaining portion 54 of the backing
layer 34. The remaining portion 54 can include a portion at the
peripheral edge 56 of the backing layer 34.
To create the impermeable portion, a sealant can be applied to the
backing layer so that the sealant permeates the backing layer. The
sealant penetrates the backing layer to plug pores, thus providing
the fluid-impermeable portion 48 of the backing layer. The sealant
can be, for example, silicone, or another polymer sealant. The
sealant may be applied in liquid form and then harden, e.g., be
cured. The sealant can be applied before or after the backing layer
is attached to polishing layer, and can be applied before or after
the window is completed.
The above described apparatus and methods can be applied in a
variety of polishing systems. Either the polishing pad, or the
carrier head, or both can move to provide relative motion between
the polishing surface and the substrate.
The polishing pad can be a circular (or some other shape) pad
secured to the platen. Terms of relative positioning are used; it
should be understood that the polishing surface and substrate can
be held in a vertical orientation or some other orientation. The
polishing layer can be a standard (for example, polyurethane with
or without fillers) polishing material, a soft material, or a
fixed-abrasive material. The entire polishing layer can be
transparent, and a portion of the opaque backing layer can be
removed to provide the window. There may be additional layers
between the backing layer and the polishing layer, or below the
polishing layer. A portion of the transparent portion may project
into the aperture in the backing layer. The aperture in the backing
layer may be larger than the aperture in the polishing layer, and
the transparent portion may be secured to a lip on the underside of
the polishing layer.
A number of embodiments of the invention have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
invention. Accordingly, other embodiments are within the scope of
the specification.
* * * * *